I have to bury speaker wires under the wooden floor being installed in my bedroom. Can any one tell me what size and where I should buy the tube which goes under the floor which will carry spaker wires? The ceiling is concrete and can not be used. The base board are inturepted by doors. Thanks.

Few non-professionals realize this, but the power available at the speakers is a function of the distance from the amp and the wire diameter. The larger the wire diameter, the better. I use ten gauge, but check your speaker and amp connectors for the maximum wire diameter that they will accept. You can always run fat wire from point to point, then attach a short length of smaller wire to make the connections to the amp and speakers if you wish.

If you want to run the wire through conduit or something like that to protect it, you would not need more than 1/2". But to be safe, you should check with whatever codes apply where you live, and use what they recommend.

By the way, there is nothing wrong with going behind the baseboards and up and over and around the doorways if it is easier or cheaper.

There is no need to get into expensive solutions like Monster Cable or any of the other tweaky variants. Regular stranded electrical wire will do. A famous Nashville studio was putting in new heavy gauge wire, and they sent welding wire at $6 a foot and fancy media wire at $125 a foot to a local lab for testing. The welding wire was made from a more pure copper. I have both 120 strand 10 gauge speaker wire and the standard 10 gauge electrical wire (which has something like 9 strands) and I cannot hear a difference.

I don't think you need any conduit, but a metal conduit will provide some shielding, but also greater capacitance that could result in some losses, especially at higher frequencies. Conduit, metal or plastic will also be handy if rodents are a problem.

Do use speaker wire and not electrical cable. You don't need the high dollar Monster Cable but a regular speaker wire will do. The gauge of the wire will be determined by the size of the amp and the distance you are running. One size larger (lower number gauge) than the minimum is a good upgrade, after that, its just extra money.